We are using macromolecular inhibition of serine protease activity to probe the role of proteases in various biological systems. Our initial protease target is urokinase-type plasminogen activator (uPA), which is thought to play a central role in the invasion and metastasis of cancerous cells. The macromolecular protease inhibitor ecotin is being engineered for specificity and activity against uPA, and these ecotin mutants are further used to identify and isolate other tumor-associated proteases. These mutant ecotins are also useful in dissecting the role of serine proteases in complex biological systems. The Computer Graphics Laboratory facilites have been invaluable in the cloning and characterization of a novel serine protease. The GCG package as well as the blast functions were used frequently. This protease appears to be overexpressed in prostate cancer and will be further characterized.